Communication relay station



July 26, 1949-. R. M. SPRAGUE ET AL COMMUNICATION RELAY STATION Filed Nov. 6, 1946 mph s zmkk w v: I

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W3 a iwss 2E whzmtq s5 ,v. g M m$ Sis R L iv 8 8 53% A e n WM o me G P ER 5% All RG said relay station to the other terminal or slave station. 77

At the slave station, the locallygenerated carrier wave, which has for example a frequency of 8030 megacycles, is mixed with the remotely last-named frequency difference controlling the.

frequency stability of said 8020 megacycle carrier wave at the relay stationfas described in the aforesaid pending application. Now, the intelligence from .the slave station is extracted, at the relay station, from the remotely-generated carrier wave at said slave station and transmitted back 130 113116 master station via the carrier Wal e of 8020 m'egacycles, the frequency of the second locally-generated carrier wave at said relay station. .At said master station the last-named carrier wave of 8020 megacycles, generated. at the relay station, mixes with the locally-generated carrier wave of the master station and the intelligence is extracted, as described in the aforementioned pending application.

In the accompanying specification there shall be described, and in the annexed drawing shown, an illustrative embodiment oflthe relay station of the present invention. It is, however, to be clearly understood that the present invention is not to be limited to the details herein shown and described for purposes of illustrationbnly, inasmuch as changes therein may be made without the exercise of invention, and within the true spirit and scope of the claims hereto appended.

. 4 W ing, as hereinbefore stated, by a predetermined frequency we. The remotely-generated carrier Wave ('1. and the intelligence wa travel along a socalled E arm I3 of a wave guide assembly I4, known as a magic T. Such a wave-guide as sembly comprises, in. addition tothe E arm I3, oppositely-disposed side branches I5.-and I6 extending in the samedirection and at right angles to the E arm I3, and a so-called H arm I1, ex-

tending outwardly from said side branches I5 and IE, and being mutually perpendiculartosaid .side branches and said E arm, said side branches,

' and is thenit'wisted through an angle of 90.

As the energy travelling along the E arm I3 from the 'horn I2 reaches the junction I8, it splits, part travelling along the side branch t6 toasec- 0nd T I9 and the other part'along the side branch I5 to a second local oscillator 20 where this part of the energy is lost.v That portion of the energy travelling along the side branch I6 enters an E armZI ofthesecondT I9.

The second-named T I9, the operation and constructionof which is fully disclosedin the copending application of George G. Bruck, en-- titled Mixingapparatus, Ser. No.- 652,628, filed March 7, 1946, now Patent No. 2,468,166, granted April 26, .1949, comprises, in addition to an H arm 22, oppositely-disposed sidebranches 23 and 24, said side branches being terminated in O positely-disposed crystals 25. and 2-6, between one. side of each of which and the T itself capaci tances 2'! and 2-8 exist, said T being grounded as shown at point 29, and said crystals being connected in series with a source 30 ofdirect current and a resistor 3|, to provide parallel outputs to ground through a capacitor 32 and the primary winding 330i a radio-frequencytransformer 34.:

' The source 30 of direct current is for the purpose In said drawing, the single figure is a partial stabilized, remotely-generated carrier wave received from a master station, or by means incorporated in the local station itself.

. This description will be addressed to the case where the carrier wave which is locally generated at a relay station is to be stabilized under the control of a carrier wave which is remotely generated at a master station.

, The. oscillator I0 is adapted to be frequency modulated, by any preferred frequency control II, as will be presently explained. An electromagnetic horn I2 is receptive, from a first predetermined direction, of a remotely-generated carrier wave of a frequency o'h, which may be frequency modulated with intelligence wa, and which emanates from a terminal station,- in the case under consideration, a master station, the master and relay carrier Waves normally differof operating the crystals 25 and 26 at a favorable point along their characteristic curve, and the series circuit is for the purpose of passing equal currents through said crystals to assure their similar. action even though they be mismatched to the wave-guide system. i

Now, as the energy of the carrier wave w'h and the intelligence wa travelling along the side branch I6 and the E arm 2I reaches a junction 35 0f the wave-guide assembly I9, assuming the electric vector of said carrier wave is pointing to the right in the E arm 2i, it splits intc two constituent waves containing-m1 and w travelling along the side branches 23 and 24, each constituent wave, respectively, travelling toward the crystals 25 and 26. The wave travelling toward the crystal 25 will haveits electricvector pointing downwardly and the wave travelling toward the crystal 26 will have its electric vector pointing upwardly. In other words, these two constituent waves will be of equal amplitude but of opposite phase.

Digressing for the. moment and referring back to the local oscillator II], it was pointed out that said oscillator provides a locally-generated carrier wave tub. The output from said oscillator is applied to one branch 3-6 of a pair of oppositelydisposed branches 36 and 31 of a third magic 'F 38, said T comprising an E arm 39, an H arm 40 and a junction 4|, all of which-are disposed in a manner hereinbefore described in connection with thefirst and second-named Ts. Y

5, he the energy travelling along the pram-c 36 reaches the junction 4' I, it splits, -par t ftravellin'g along the n arm n to anatten-uator 42 andithe "other part loein'g radiatedurrcm -electromag netic hem 53, as will b'e explain'ed below. lIhe attenuator perm-its just --enough of said partial energy from said local oscillator it to travel along the "H arm 22 to the junction where said energy again splits into tw'o --oonstituent waves w the Waves traveling along the side branches 23 -24, respectively, to- Ward 'the -orysta1s :25 and 26. Assuming that the electric vector of the wave wh travelling along the H arm :22 is pointin u wardly-at theiun'c- 'tion 35, -the=cons'tituent waves thereof travelling along the side branches :23 ana 2-4 will have *their "electric Vectors, :likewise, pointin upwardly. In other words, these consti'tuent waves will he or equal amplitude and like "phase. i At the crystals 25 and 25, there :are now :present in-phaseportionspf tlre locally generated carrie'r Wave-um, out of phaseiportions of the remotely-generated carrier ii/ave w'h and theintelligence we. Therefore, at the crystals 2.5 am 2 6 'there are produced two waves having a beat frequency,

whose frequency corresponds to the frequency diiierenc'ewdbetween the carrier waves. At the crystal 26, the resultant wave is produced by two in-phase components and the phase of "said resuite-int wave may' thus=oe considered positive. At

the crystal 2 6, the resultant wave is produced by two out of-phase components and the phase of said l'astmamedxresultantwave may thus be-consldered negative. However, inasmuch as parallel outputs are taken from the crystals 25 and 25, the two resultant wavesarein-phase with respect wd bEtWE'E'H the frequencies of "the locally and remdtely-generated carrier WaVBSwn and-'wn. The output of the amplifier 44, consisting of the dif- 'ference frequency we and any audio-frequency n'ioc'lula'ti'on or iritelligence wa, originating at the master-station, is appliedtoa mixer. Also ap- "plied to said mixer is a frequency-modulated "sig nal-wmfrom a monitoring oscillator 46. This last named monitoring unit enables the relay station operator to break in on thetransmission being relayed *in the event of emergencies, etc. The '10- pally-generated intelligence w'a is applied to said monitoring oscillator 46 through a microphone Wand an audio-frequency transformer 48, "the operation ofthe microphone 41 being controlled by a switch 49.

At the mixer the frequencies we and mm are combined to produce a second difierence'freuuen- Gy'w'd, theoutput from said mixer being applied 'to'asecond broadband amplifier 50, whose centerfrequency corresponds to the difference frequency w'e; "The output of the amplifier 50, consisting of the second difference frequency w'd and "any *audioirequency modulation we and w'eorigin'ating, respectively, at the "master station or relay station, is applied "to a frequency "discriminator "511 w hosecenter frequency corresponds to the dir- :ferencefrequency w's. The discriminatorextraots therinitelligencem ore/e impressed-'uponthe diiferenoe frequency-o t input applied thereto, which intelligence is then conveyed simultaneously to an 6, aimio nequency amplifier :52 and the frequency control I l.

'iirhe patput irrcmnthe 'trequeney control It! tre: quency modulates the local oscillator ['0 and the energy :from Isaid oscillator travels along "the branch arm 36 and thence to the junction 11 where n splits, par-t travelling alon the H :arm it as explained hereinb'e fore, the other part travellii'i g aIong'the'E-arm -39 to the electromagnetic horn 53 wh-ichfis adapted "to directionally radiate the 'carrier oii containing we or uia.

ine'garding "the intellig 'ence conveyed to the audi0-frequency amplifier 52, the output of s'aid amplifiei is applied-to an audio-frequency translormer st and then cc to zah'ones '55. The functibn oi-said last nain ed componerits serves as anion-itoning imit to su ervise the relayed transmission by-anoperator at the r'ei'ay station.

ns iongas the mean frequency or the interl ne -diatefrequency wave derived from the heterodynin ci th'eremotely and locally-generated car'- :rier waves corresponds to the predeterll'iihd dif- Terence Md thereb'etween, the only output froln the discriminator 5i is an audio-frequency -ou tp-lit corresponding to the intelligence weo'r Us. Howevorshciild thecscillator to drift, vresulting in a tiev'iati olrof the nequ'ene "of t e intermediatefrequency wave "from the difference nee-hence ea i'aetween the carrier-wave frequencies, the discriminator til will have an :out ut including, in additionto-thatresultin-gironi the intelligence'applied thereto, a D.-'-C. or -unidire'otional ccmpd nent whose sense and magnitude Willdepen'd, respectively, on the sense and magnitude of any such deviation. Therefore, the output of the 'discrimina'tor is applied to the frequency control -H to'adi-ustthe oscillator i 0 and compensate for any frequency deviation from the mean frequency desired 'ofsaid oscillator.

Thus far there has been described that portion ofthe relaystati'on oithepresentinvention when said station is relayingthe transmission, represented by wh ma, received from the master station at the (electromagnetic horn 12. Under these conditions thesystem'per'forrhs like a single repeater ma station. However, the relay station or the "present invention is capable 'of relaying, in two different directions, two difie'reii't remotely-generated carrier waves simultaneously, the components and'the operational functions'be ing the same when "the other terminal or-slave stationtransmits toward the electromagnetic horn 53 a remotely-generated carrier wave w h con taining intelligence (We.

A locally-generated carrier wt .produced'by a local oscillator 2B combines with the remotely generated carrier wave w"h to produce a difference frequency w d in a fourth magic T "56 in the same manner described in connection with the first-named local oscillator 10. 'The output of a pair of oppositely-disposed crystals '57 and 58 'is applied, as explained hereinbefore in connection with the magic "1" [9, through a capacitor-59 and thence 'tothe primary 6!! of a radio-frequency transformert'l. explained previously, the output of thera'dio-frequency transformer is applied to'a series "of stages, 62, 63, E4, 65, 66, '61, 68 and '63 and tothe local oscillator!!! in the same man-- ner in connection with the stages 4 8- 45 and stage H.

The intelligence t"s having been extracted in "the same manner as the intelligence ms, and w'e, said intelligencefrequency modulatesthe local oscillator 20; "whereby the locally-generated carrierwave e s containing the remotely-gem erated intelligence We is radiated from the horn purposes.

This completes the description of the aforesaid illustrative embodiment of the present invention, including the mode of operation thereof either as a one-way or two-way relay station in a communication system having the characteristics a chain of relay systems as presented in this specification.

What is claimed is: r

1. In a relay station for a communication system:. means for locally generating a carrier wave; means for receiving a remotely-generated carrier wave, said carrier waves normally having a predetermined frequency difference therebetween means, receptive of portions of both said 1 carrier waves, for deriving from one, two constituent waves of equal amplitude and opposite phase, and from the other, two constituent waves of equal amplitude and like phase; means for deriving from all of said constituent waves an intermediate-frequency wave whose frequency normally corresponds to said predetermined difference between the frequencies of said carrier waves; means, receptive of said intermediatefreq'u'ency wave, for deriving therefrom a unidi- 'rectional output whose sense and magnitude are functions, respectively, of the sense and magnitude of any deviations of thefrequency of said intermediate-frequency wave from said predetermined difference between the frequencies of said carrier waves; means, receptive of said unidirectional output, for so controlling the frequency of said locally-generated carrier wave in response thereto as to maintain substantially constant said predetermined difference between the frequencies of said carrier waves; and means for transmitting said locally-generated carrier wave.

2. In a relay station for a communication system: means for locally generating a carrier wave;

means for receiving a remotely-generated carrier wave, said carrier waves normally having a predetermined frequency difference therebetween; means, receptive of a portion of one of said carrier waves, for dividing the same into two constituent waves of equal amplitude and opposite phase; means, receptive of a portion of the remaining carrier wave, for dividing the same into two constituent waves of equal amplitude and like phase; means for mixing said firstnamed constituent waves, respectively, with said second-named constituent waves to derive therefrom two beat-frequency waves of equal amplitude and opposite phase; means for so combining said beat-frequency waves as to produce a single intermediate-frequency wave whose frequency normally corresponds to said predetermined difference between the frequencies of said carrier waves; means, receptive of said intermediate-frequency wave, for deriving therefrom aunidirectional output whose sense and magnitudeare functions, respectively, of the sense and magnitude of any deviations of the frequency of said intermediate-frequency wave from said predetermined difference between the frequencies of said carrier waves; means, receptive of said unidirectional output, for so controlling the frequency of said locally-generated carrier wave in,

response thereto as to maintain substantially constant said predetermined difference between the frequencies of said carrier waves; and means for transmitting said locally-generated carrier wave.

3. In a relay station for a communication system: means for locally generating a carrier wave; means for receiving a remotely-generated carrier wave, said carrier waves normally having a predetermined frequency difference therebetween; means, receptive of portions of both said carrier waves, for deriving from one, two constituent waves of equal amplitude and opposite phase, and from the other, two constituent waves of equal amplitude and like phase; means for deriving, from all of said constituent waves an intermediate-frequency wave whose. frequency normally corresponds to said predetermined difference between the frequencies of said carrier,

waves; means, receptive of said intermediatefrequency wave, for driving therefrom an output for so controlling the frequency of said locallygenerated carrier wave as to maintain substantially constant saidpredetermined difference between the frequencies of said carrier waves; and means for transmitting said locally-generated carrier wave. V

- 4. In a relay station for a communication system: means for locally generating a carrier wave; means for receiving a remotely-generated carrier wave, said carrier waves normally having a predetermined frequency difference therebetween; means, receptive of a portion of one of said carrier Waves, for dividing the same into two constituent waves of equal amplitude and opposite phase; means, receptive of a portion of the remaining carrier wave, for dividing same into two constituent waves of equal amplitude and like phase;

means for mixing said first-named constituent waves, respectively, with said second-named constituent waves to derive therefrom two beatfrequency waves of equal amplitude and opposite phase; means for so combining said beat-frequency waves as to produce a single intermediatefrequency wave whose frequency normally corresponds to said predetermined difference between the frequencies of said carrier waves; means, receptive of said intermediate-frequency wave, for deriving therefrom an output for so controlling the frequency of said locally-generated carrier wave as to maintain substantially constant said predetermined difference betweenthe frequencies of said carrier waves; and means for transmitting said locally-generated carrier wave.

I 5. In a relay station for a radio communication system: ,means for locally generating a carrier wave; means for receiving a remotely-generated, frequency-modulated carrier wave, said carrier waves having a predetermined frequency difference therebetween; means, receptive of said locally-generated carrier wave and said remotelygenerated, frequency-modulated carrier wave, for deriving from one, twoc-onstituent waves of equal amplitude and opposite phase, and from the other, two constituent waves of equal amplitude and like phase; means for deriving from all of said constituent waves a frequency-modulated, intermediate-frequency wave whose mean frequency area-sec cor-respcnds to the (inference between: the: frequency oi said'i locallgngeneratedi carrier wave and the mean frequency: of said: remotely-generated carrier waveg: means, receptive efi said inter mediate frequency wave, for extracting therefrom the intelligence incenponat'ed therein; means, receptive oi? said intelligence; for altering the frequency of said locally-generated carrier wave inz accordance therewithr andmeans for transmitting the resulting frequency modulat'edi locally-generated carrier wave.

6a In a: relay, station for a radio communicaticn systems meam ion locally generating a carrier: wave; means for receivinga remotel w generated, frequencwmcdulated carrier wave; said carrier wanes: a: predetermined frequency;dlfference-tlienebetweenr means, receptive of a portion: of (ma oi? carrier waves; for dividing; the! same. into: two; constituent waves of equal amplitude and" opposite phase; means, receptinesofa portiomoi theremainingcanrierwava fen dividing the same; into: two constituent: waves of: equal: amplitude and like phase means for mix ingasaidi first-named; constituent waves, respectively, with, said seconds-named constituent wanes; to deriue theretmrm two: beat-frequency waves. equal; amplitude-i and: opposite phase; means fer-smcomhiming saidlbeatiirequency waves as to produce a; single irrtermediateefrequency wave: whose frequency. nnmnallyv corresponds: to thedifference: between the frequency or said locally-generated: carrier: wave and the mean frequency ofi saidrremotely genenatedi carrier waves; means; receptive; of: said intenmediate frequency wave; for extracting therefrom the intellig encei incorporated: therein; means; receptive of said intelligence; for altering the frequency of said; locally-generated: earlier wave: in: accordance therewith andimeans for'transmittingthe resulting; frequency-modulatem. lonallie-gen-eratedi car rier wave. c

7r Ina nelau'statimi tor airadio communication system: means: ion locally; gemmating a.v carrier wavm. means ion receiving a remotely generated, firequencwmodulated; carried waster said. carrier waves having; a predetermined: frequency diflem ence therebctweeni; means, receptive of! said locally-generatedeanrier'wauesandlsaicrremotelygenerated, frequencnemndnlatedi carrier wave; for deriving ironstone; two; constituentnvaues of; equal amp litude. andlepnesitea phase ramtirom: the: other, two. constituent, waves Oil equar mnplitudeand; like phase means for deriving: from ofisaidt constituent waves a finequencyamedmamd; intermediateefrequency: wave whose: mean frequency corresponds; to the dilfiereme; betweensthe frequency of: said! lccallwgenemteda carnienwaive: and the mean inequencyct. said: remntely generated carrier wavm, means receptive: (If? said; intermediato -frequencywavegtonextracting;therefrom theintelligence incorporated therein; means, receptive of said! intelligcncaifior altening the frequency of said local-lyegenenatedi carrier wave: in accordance therewith;, and; for transmitting the; resulting frequency-modulated; locallyeneratedi carrier wane.

al In a relay-station; for a: radio-communication system; means. for locally generating-a carrier wave; means for. receivm a remoitely generatedg frequency-modulated carrier: wave; said: carrier wane havin a: Hmdetenminmh firequency' difler- 'ence therehetweentj means; neceptiue are, portion of; one oil said: carrier: waves, for dividing the same,- into; two cmastituent waves; of? equal: amplitude and opposite; phases: means; receptive of a portion-- of the remainingcarrier' wave; for dividiingsame intotwo constituent wavesof equal amplitude and like phase; means: for mixing said first n-amed constituent "Waves, respectively, with said second-named" constituent waves. to derive therefrom two beat-frequency waves of; equal amplitude and; opposite hase; means. for solcombining said beats frequency waves as to: produce asingle intermediate-frequency' wave -whose mean frequency corresponds to the difierence between the frequency of" said locally-generated; carrier wave and: the mean frequency of said remotely.- generated carrier wave; means receptive" 015 said intermediate frequency wave, for extracting therefrom. the intelligence incorporated therein; means,lreceptive ot'said intelligence, for the. frequency: oh said locally generated: carrier wave inaccordance therewith; and; means; for transmitting.- the resulting frequency-modulated, locally-generated: carrier wave;

9.x In a relay station for acommunicationsystem: meanszfor locally: generating. a: carrier: wave; means for receiving a remotely-generated; free quency.'- mo'dulated carried wave, said cashier waves normally having a predetermined: free quency difference therebetween; meansiiorcombining said locally generated; carrier wave with said remotelyegenerated frequencwmodulated carrier wave, for deriving fromlone, two constitlrr ent waves of equal; amplitude; and opposite phase, and from the other two; constituent waves. of equal: amplitude and like; phase; means; for: (let ri-vingfrom; all of said! constituent. waves. at frequency-modulated;v intermediate frequency wave whose mean frequency corresponds to the difference between the frequency of. said locallygenerated' carrier wave and the mean: frequency of" said: remotely-generated carrier. wave; means receptive of said intermediate-frequency WEWB, for derivingtherefrom an output: Wave; the magnitude. and; sense of which corresponds to: the magnitude andl sense of theideviation of": the frequency of: said intermediate frequency; wave from; its mean; frequency and: for extracting therefrom the. intelligence incorporated; therein; means, receptive of; said: output. wave and said intelligence, for controlling the frequencyof said locally-generated carrier wave as: to maintain substantially constant said predetermined difference between; the mean frequency of said: remotely -generatedicarrier wave and; the frequency of: said local carrier waive and to; incorporate in the latter said intelligence; and" means for trans mitting the resulting frequency=modulated lo eally generated: carries wave.

10; In: a: relay stationfor a communication sys-- tem: meanszfor locally generating a carrierwave; meansfor receivin a: remotely-generated, irequency modulated carrier wave; said. carrier waves normally having a predetermined frequency difference therebetween; means; receptive ofa: portion of one ofsaid carrier waves, for dividing; the same into two constituent waves oh equal: amplitude and opposite phase; means, receptive of a portion of the remaining carrier wave; for dividing the same into two-constituent waves of equal amplitudeand like phase; means for mixing said first named constituent: Waves, respectively, with said: second-named constituent' waves to derive there-from two beat-fre quency waves of" equal amplitude and opposite phase; means for so combining said beat-frequency-waves as to produce a single intermediate-frequency wave whose mean frequencvcorresponds to-the difterence between the frequency rated therein; imeans, receptive of said output wave and said intelligence, for controlling the frequency of said locally-generated carrier'wave as to maintain substantially constant said predetermined diiference between the mean frequency of said remotely-generated carrier wave and the frequency of said local carrier wave and to incorporate in the latter said intelligence; and means for transmitting the resulting frequencymodulated, locally-generated carrier wave.

11. In a relay station for a communication system: means for locally generating a carrier wave; means for receiving a remotely-generated, frequency-modulated carrier wave, said carrier waves normally having a predetermined frequency difference therebetween; means for combining said locally-generated carrier wave with said remotely-generated, frequency-modulated carrier wave to derive from one, two constituent waves of equal :amplitude and opposite phase,

and from the other, two constituent waves of equal amplitude'and like phase; means for deriving from all of said constituent waves a frequency-modulated, intermediate-frequency wave whose mean frequency corresponds to the diiference between the frequency of said locally-gen- 3;;

erated carrier wave and the mean frequency of' said remotely-generated carrier wave; means receptive of said intermediate-frequency wave, for deriving therefrom an output wave, the magnitude and sense of which corresponds to the magnitude and sense of the deviation of the frequency of said intermediate-frequency wave from its mean frequency and for extractin therefrom the intelligence incorporated therein; means,

receptive of said output wave and said intelli- 745 gence, for controlling the frequency of said 10- cally-generated carrier wave as to maintain substantially constant said'predetermined difference between the mean frequency of said remotelygenerated carrier wave and the frequency of said local carrier wave and to incorporate in the latter said intelligence; and means for transmitting the resulting frequency-modulated, locally-generated carrier wave.

12. In a relay station for a communication 5- 55 tem: means for 'locally generating a carrier wave; means for receiving a remotely-generated, frequency -modulated carrier wave, said carrier waves normally having a predetermined fre quency diiferenee therebetween; means, receptive 0 of a portion of one of said carrier waves, for di viding the same into two constituent waves of equal amplitude and opposite phase; means, receptive of a portion of the remaining carrier wave, for dividing same into two constituent waves of equal amplitude and. like phase; means for mixing said first-named constituent Waves, respectively, with said second-named constituent waves to derive therefrom two beat-frequency waves of equal amplitude and opposite phase;

means for so combining said beat-frequency waves as to produce a frequency-modulated, intermediate-frequency wave whose mean frequency corresponds a; the difference between the frequency of said"locally-generated carrier wave and the'mean, frequency of said remotelygenerated carrier wave; means receptive of said intermediate-frequency wave, for deriving therefrom an output wave, the magnitude and sense of which corresponds to the magnitude and sense of the deviation ofthe frequency of saidintermediate=frequeney wavefrom its mean; frequency and for extracting therefrom the intelligence incorporated therein; means, receptive of said output wave and said intelligence, for controlling the frequency of said locally-generated carrier wave as to maintain substantially constant said predetermined difference between the mean frequency of said remotely-generated carrier wave and the frequency of said local carrier wave and to incorporate'in the latter said intelligence; and means for transmitting the resulting frequencymodulated, locally-generated carrier wave.

13. In a relay station for a communication system: a plurality of double T-ishaped wave-guide assemblies, each including across arm common to both of itsTs and a pair of branch arms perpendicular to said cross arm and to each other; means, connected to one of the branch arms of two of said wave-guide assemblies, for receiving andradiating electromagnetic carrier waves; a carrier-wave generator'connected to one end of the cross arm of each of said 'last named waveguide assemblies; the other end of said lastnamed cross arms being connected to one of the branch arms of two other of said wave-guide assemblies; the remainingbranch arms of said first'two wave-guide assemblies being connected to the remaining branch arms of said second two wave-guide assemblies; said first two waveguide assemblies being receptive, respectively, of remotely-generated carrier waves to divide the same, respectively, into two constituent waves, one of each of said constituent waves entering, respectively, said second two wave-guide assembliesto divide the same, respectively, into two sub-constituent Waves of opposite phase; said first two wave-guideassemblies being alsoreceptive of locally-generated carrier waves to divide the same, respectively, into two constituent waves, one of each of said last-named constituent waves entering, respectively, said second-named waveguide assemblies and the other of each of said last-named l constituent waves being transmitted in the respective directions from which said remotely-generated carrier waves were received, the

of said last-named constituent waves enteringsaid second-named wave-guide assemblies and dividing into sub-constituent waves of like phase; a pair of series-connected, oppositely-disposed non-linear impedances terminating the opposite ends of the cross arms of said second two wave guide assemblies for combining said locally and remotely-generated, sub-constituentwaves to derive therefrom intermediate-frequency waves; an inductive impedance connected in parallel with each pair of said non-linear impedances for extracting said intermediate-frequency waves; and means, receptive of said intermediate-frequency waves, for so controlling the frequencies of said locally-generated carrier waves, respectively, as to maintain substantially constant predetermined differences between the frequencies of said locally and remotely-generated carrier waves.

14. In a relay station for a communication system; means for locally generating a carrier wave; means for receiving a remotely-generated carrier wave, saidcarrier waves normally having a predetermined frequency diiference therebetween; means, receptive of portions of both of said carrier waves, for deriving therefrom a first intermediate-frequency wave whose frequency nor mally corresponds to said predetermined difference between the frequencies of said carrier waves; means for locally generating a monitoring wave; means, receptive of said first intermediate-frequency wave and said monitoring wave, for deriving therefrom a second intermediatefrequency wave; means, receptive of said second intermediate-frequency wave, for deriving therefrom a unidirectional output whose sense and magnitude are functions, respectively, of the sense and magnitude of any deviations of the frequency of said first intermediate-frequency wave from said predetermined difference between the frequency of said carrier waves; means, receptive of said unidirectional output, for so controlling the frequency of said locally-generated carrier wave as to maintain substantially constant said predetermined difference between the frequencies of said carrier Waves; and means for transmitting said locally-generated carrier wave.

15. In a relay station for a communication system: means for locally generating a carrier wave; means for receiving a remotely-generated carrier wave; said carrier waves normally having a predetermined frequency difference therebetween; means, receptive of portions of both of said carrier waves, for deriving therefrom a first intermediate-frequency wave whose frequency normally corresponds to said predetermined difference between the frequencies of said carrier waves; means for locally generating a monitoring wave; means for frequency modulating said monitoring wave in accordance with locallygenerated intelligence; means, receptive of said first intermediate-frequency wave and said monitoring wave, for deriving therefrom a secondfrequency-modulated intermediate-frequency wave; means, receptive of said second intermediate-frequency wave, for deriving therefrom a unidirectional output whose sense and magnitude are functions, respectively, of the sense and magnitude of any deviations of the frequency of said first intermediate-frequency wave from said predetermined difference between the frequencies of said carrier waves and the sense and magnitude of the deviations of the frequency of said monitoring wave due to the frequency modulation of said monitoring wave; means, receptive of said unidirectional output, for so controlling the frequency of said locally-generated carrier wave as to maintain substantially constant said predetermined difference between the frequencies of said carrier waves and simultaneously to frequency modulate said locally-generated carrier wave in accordance with said locally-generated intelligence; and means for transmitting said locally-generated carrier wave.

ROBERT M. SPRAGUE.

GEORGE G. BRUCK.

PHILIP E. VOLZ.

REFERENCES CITED The following referenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,148,532 Chaffee Feb. 28, 1939 2,369,268 Trevor Feb. 13, 1945 2,408,791 Magnuski Oct. 8, 1946 FOREIGN PATENTS Number Country Date 116,110 Australia Nov. 4, 1942 Certificate of Correction Patent No; 2,477,428 July 26, 1949 ROBERT M. SPRAGUE ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 10, line 24:, claim 9, for the word carried read carrier; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed t 's 13th day of December, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

